I 136 APPENDICKS AND TABLES USEFUL TO THE MICROSCOPIST 



4 grammes = 15 (drachm) (apothecaries') ; 7 grammes = 4 dr. (drachms) 

 (avoirdupois). 



5 kilogrammes = 11 Ib. (avoirdupois). 



50 kilogrammes = 1 cwt. 



NoberVs 19 Band Test Plate 

 Band Lines per inch Band Lines per inch 



1 11259-5 



15 90076-1 



19 112595-1 



5 33778-5 



10 61927-3 



Difference between each band = 5629-75. 



Nobert's last 20 Band Test Plate 

 Band Lines per inch Band Lines per inch 



1 11259-5 



5 56297-6 



15 168892-7 



20 225190-3 



10 112595-1 



Difference between each band = 11259'u. 



Convenient Formula for Lantern Projection or Enlargement and 



Reduction. 



Let D be the distance of the screen, and d the distance of the object 

 from the optical centre of the lens, F the equivalent focus of the lens. M 

 the magnifying power or ' number of times ' for enlargement or reduction, 

 then 



D-ECH*,,; ,-;**-, l-^K-^l, 



Example : It is required to project by a lens of 6 inches equivalent 

 focus a slide having a 3-inch mask so that it may give a 10-ft. disc, what 

 must be the distance of the screen ? Here M the magnification will be 

 40 times. D = F (M + 1) = 6 (40 + 1) = 246 inches = 20i feet. 



Note, in a double combination the optical centre may be assumed to 

 be half way between the lenses. To reduce, interchange the object and the 

 screen. 



Royal Microscopical Soi-irtifs (./"/ //r.v 



Substage 1-527 inch = 38-786 mm. 



Eyepieces. No. 1 -9173 -_|:;-:500 



2 1-04 =26-416 



3 1-27 -32-258 



4 1-41 =35-814 ,. 



For the screw of the objective and nose-piece the Society supply, at 

 cost price, a sizing die and plug, also screw chasers. They d'o not, how- 

 ever, supply standard screw gauges. Full particulars regarding the 

 screw will be found in the 'E.M.S. Journal,' IS'.u;. p. :i89. 



